A measuring device for gas analysis, in which test gas is admitted to the gas sensor of a measuring head by means of a measured gas pump, is known from DE 102 31 515 C1, which corresponds to U.S. Pat. No. 6,701,773 which is incorporated by reference. A plug-in adapter, which has individual gas ducts, via which measured gas is drawn in by means of the measured gas pump and is delivered to the gas-specific surface of the gas sensor, is connected to the measuring head.
The prior-art gas-measuring device is also suitable for detecting volatile substances, which are adsorbed by the pump diaphragm of the measuring gas pump. The plug-in adapter is attached for this to the measuring head such that the gas sensor is located in front of the measured gas pump and is directly exposed to the volatile substance.
The prior-art gas-measuring device is suitable for continuous gas sampling, during which measured gas is drawn from a gas source.
A function test can be carried out with the prior-art gas-measuring device only by connecting it to a test gas source. Carrying along test gas sources makes handling difficult, especially because a simple function test, to be performed to determine whether or not a gas-measuring device responds to a certain gas, is sufficient in many cases.
Multi-gas-measuring devices, with which different components in a gas sample can be detected simultaneously, are known. Such multi-gas-measuring devices contain different measuring systems, in which infrared optical, electrochemical or catalytic detection methods are used. Multi-gas-measuring devices are often also designed as compact, portable measuring devices, which can simply be carried along and perform the gas concentration measurement directly at a possible hazard site.
The calibration of such gas-measuring devices for combustible materials with high-boiling hydrocarbons such as nonane and xylene is very complicated and cumbersome according to the current state of the art. Nonane is used as an additive in motor fuels, is readily combustible and has a gasoline-like odor. It is known to use, e.g., a calibration chamber for this, in which a certain quantity of liquid is dispensed into a known chamber volume by means of a plunger syringe and evaporated. The device to be calibrated is connected to the chamber. At the same time, a fan present in the chamber must be started in order to swirl the vapor. Handling requires utmost care because possible leaks in the chamber or errors in dispensing the liquid may lead to incorrect calibration. The high-boiling hydrocarbons evaporate very slowly at low ambient temperatures and lead to additional errors.
If the so-called saturated vapor calibration is used, relatively large quantities of liquid must be dispensed into the calibrating volume and ventilated there until a maximum vapor pressure becomes established, which depends on the temperature only. This temperature is measured with an additional temperature measuring device, and the concentration is determined from corresponding charts or diagrams.